Administering an injection is a process which presents a number of risks and challenges for users and healthcare professionals, both mental and physical.
Injection devices (i.e. devices capable of delivering medicaments from a medication container) typically fall into two categories—manual devices and auto-injectors.
In a manual device—the user must provide the mechanical energy to drive the fluid through the needle. This is typically done by some form of button/plunger that has to be continuously pressed by the user during the injection. There are numerous disadvantages to the user from this approach. If the user stops pressing the button/plunger then the injection will also stop. This means that the user can deliver an underdose if the device is not used properly (i.e. the plunger is not fully pressed to its end position). Injection forces may be too high for the user, in particular if the patient is elderly or has dexterity problems.
The extension of the button/plunger may be too great. Thus it can be inconvenient for the user to reach a fully extended button. The combination of injection force and button extension can cause trembling/shaking of the hand which in turn increases discomfort as the inserted needle moves.
Auto-injector devices aim to make self-administration of injected therapies easier for patients. Current therapies delivered by means of self-administered injections include drugs for diabetes (both insulin and newer GLP-1 class drugs), migraine, hormone therapies, anticoagulants etc.
Auto-injectors are devices which completely or partially replace activities involved in parenteral drug delivery from standard syringes. These activities may include removal of a protective syringe cap, insertion of a needle into a patient's skin, injection of the medicament, removal of the needle, shielding of the needle and preventing reuse of the device. This overcomes many of the disadvantages of manual devices. Forces required of the user/button extension, hand-shaking and the likelihood of delivering an incomplete dose are reduced. Triggering may be performed by numerous means, for example a trigger button, the action of placing the autoinjector against the skin or the action of the needle reaching its injection depth. In some devices the energy to deliver the fluid is provided by a spring.
Auto-injectors may be disposable or single use devices which may only be used to deliver one dose of medicament and which have to be disposed of after use. Other types of auto-injectors may be reusable. Usually they are arranged to allow a user to load and unload a standard syringe. The reusable auto-injector may be used to perform multiple parenteral drug deliveries, whereas the syringe is disposed after having been spent and unloaded from the auto-injector. The syringe may be packaged with additional parts to provide additional functionality.
US 2002/0095120 A1 discloses an automatic injection device which automatically injects a pre-measured quantity of fluid medicine when a tension spring is released. The tension spring moves an ampoule and the injection needle from a storage position to a deployed position when it is released. The content of the ampoule is thereafter expelled by the tension spring forcing a piston in a proximal direction inside the ampoule. After the fluid medicine has been injected energy stored in the tension spring is released and the injection needle is automatically retracted back to its original storage position.
In order to prevent post-injection needle stick injuries, syringes with needle retraction have been developed. These syringes comprise a stopper, a plunger connected to the stopper, a hollow injection needle and a needle retraction spring. When the stopper in such a syringe has bottomed out and displaced at least nearly all of the syringe's content it grips a part of the needle protruding into the interior of the syringe. The needle retraction spring pushes the plunger in distal direction, i.e. away from the injection site. The plunger then pulls the stopper and the needle in distal direction until the needle is hidden inside the syringe.
GB 2 447 339 A discloses an autoinjector comprising an outer housing in which is mounted a syringe comprising a barrel for holding a volume of medicament, a needle at one end of the barrel and a plunger axially-moveable in the barrel, the autoinjector further comprising an inner housing intermediate the outer housing and the syringe and an energy source in communication with said inner housing, wherein the inner housing is moveable by the energy source between three positions, namely a first position in which the inner housing is in communication with the barrel such that, in use, the plunger and barrel are moveable axially so as to move at least part of said needle out of the outer housing; a second position in which the inner housing is in communication with the plunger but not the barrel such that, in use, said plunger is moveable axially into said barrel so as to expel medicament through the needle; and a third position in which the inner housing is in communication with neither the plunger nor the barrel such that, in use, the plunger and barrel are able to retract in order to retract the needle into the outer housing, characterised in that the plunger includes biasing means for axially biasing the barrel, before activation of the energy source, to a position forward of the part of the inner housing which acts on the barrel in said first position.
US 2003/105430 A1 discloses an automatic injector in which the needle is injected automatically into the injection site (e.g., a patient's skin), delivery is initiated upon activation of the injector, and the needle is retracted after the end of delivery. Preferably the needle is not seen by the user prior to, during or after injection. Prior to and after injection, the needle is withdrawn into the device so as to avoid any potential injury or health risk to the user or health care provider. The injector includes a housing and a control unit arranged to slide within the housing to move a piston rod during drug delivery and to pivot within the housing for needle retraction. The injector may also include a back rod that moves the piston rod before activation of the injector for titration and reconstitution and automatically disengages from the piston rod upon activation of the injector. A needle-locking device can be used in any number of pen-like injectors or other types of injectors or syringes. The needle-locking device includes a clip that insures that a needle assembly within an injector is in a locked position before and after use.